A blown fuse can cause your fuel gauge and speedometer to stop working. Replace the fuse. The fuse can be found in the fuse box. The location of the fuse will be listed on the inside cover of the fuse box.
First check the fuse for the 2003 Cavalier gauge. Next check the fuel sending unit in the fuel tank to insure that its working properly. Check the gauge next, then the wiring for the system. One of these units is causing your gauge to not work.